How do you handle account bans? If someone buys your account and gets banned, then all the accounts get compromised as there is no way to know for sure that the account was really sold.
I have sold accounts in the past where the buyer immediately started making dozens of spammy posts, and was quickly banned. None of my other accounts were affected. I think it is pretty fair to say that BadBear is pretty good at detecting when an account was sold.
I had that question following this thread
https://bitcointalk.org/index.php?topic=994097.0IMO banning everyone, seller, buyer is the right thing to do as one can never be sure that the account has indeed been sold. You would obviously disagree to this, but not doing this creates a loophole.